Apparatus and method for reducing average scan rate to detect a conductive object on a sensing device

ABSTRACT

A switch circuit and method is described. In one embodiment, the switch circuit is configured to couple each of a plurality of plurality of capacitive sense elements and a plurality of capacitance sensors in different modes. In a first mode, the switch circuit is configured to couple each of the plurality of capacitance sensors to a group of two or more of the plurality of capacitive sense elements. In a second mode, the switch circuit is configured to couple the plurality of capacitance sensors to individual ones of the two or more of the plurality of capacitive sense elements in one of the groups.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/948,885, filed Jul. 23, 2013, which claims priority to U.S.application Ser. No. 13/047,035, filed Mar. 14, 2011, now U.S. Pat. No.8,493,351, issued Jul. 23, 2013, which claims priority to U.S.application Ser. No. 11/396,179, filed on Mar. 30, 2006, now U.S. Pat.No. 8,144,125, issued Mar. 27, 2012, all of which are incorporated byreference herein their entirety.

TECHNICAL FIELD

This invention relates to the field of user interface devices and, inparticular, to touch-sensing devices.

BACKGROUND

Computing devices, such as notebook computers, personal data assistants(PDAs), and mobile handsets, have user interface devices, which are alsoknown as human interface device (HID). One user interface device thathas become more common is a touch-sensor pad. A basic notebooktouch-sensor pad emulates the function of a personal computer (PC)mouse. A touch-sensor pad is typically embedded into a PC notebook forbuilt-in portability. A touch-sensor pad replicates mouse x/y movementby using two defined axes which contain a collection of sensor elementsthat detect the position of a conductive object, such as finger. Mouseright/left button clicks can be replicated by two mechanical buttons,located in the vicinity of the touchpad, or by tapping commands on thetouch-sensor pad itself. The touch-sensor pad provides a user interfacedevice for performing such functions as positioning a cursor, orselecting an item on a display. These touch-sensor pads can includemulti-dimensional sensor arrays. The sensor array may be onedimensional, detecting movement in one axis. The sensor array may alsobe two dimensional, detecting movements in two axes.

FIG. 1A illustrates a conventional touch-sensor pad. The touch-sensorpad 100 includes a sensing surface 101 on which a conductive object maybe used to position a cursor in the x- and y-axes. Touch-sensor pad 100may also include two buttons, left and right buttons 102 and 103,respectively. These buttons are typically mechanical buttons, andoperate much like a left and right button on a mouse. These buttonspermit a user to select items on a display or send other commands to thecomputing device.

FIG. 1B illustrates a conventional touch-sensor pad. The touch-sensorpad 100 includes a plurality of metal strips 104(1)-104(N), where N isthe number of strips. The plurality of metal strips 104(1)-104(N) atecoupled to the processing device 105, including a plurality ofcapacitance sensors 103(1)-103(N). The plurality of metal strips104(1)-104(N) are configured to determine the location or position ofthe conductive object 106. For ease of discussion and illustration, onlythe N parallel running metal strips in only the Y direction (e.g., todetect motion in the x-direction) of the touch-sensor pad 100 have beenincluded. In this conventional design, each capacitance sensor 103 iscoupled to a corresponding metal strip 104. In other words, for eachsensor element 104, the processing device 105 has a corresponding pin toconnect each strip of the touch-sensor pad to the processing device 105.Accordingly, this conventional design uses linear search algorithms todetermine the position of the conductive object 106 on the plurality ofmetal strips. With a linear search algorithm, capacitance variation isdetected one by one in a linear fashion. By comparing the capacitancevariation between the baseline and the capacitance variation onneighboring metal strips, the position of the conductive object 106(e.g., X coordinate) is determined. For example, the processing device103(1) may first detect the capacitance variation on the first metalstrip 104(1), then 104(2), and so on, until in detects the conductiveobject on the seventh metal strip 104(7). If the conductive object is onthe first metal strip 104(1), then the processing device 105 only takesone cycle to detect the conductive object 106. If the conductive objectis on the N^(th) metal strip 104(N), then the processing device 105takes N cycles to detect the conductive object 106. Accordingly, theprocessing device 105 takes, on average, (N+1)/2 to locate thecontacting point of the conductive object 106 with this linear searchingalgorithm.

In conventional touch-sensor pads using a PS/2 interface, the scan rateor speed at which the touch-sensor pad locates the position of thecontact point of the conductive object on the touch-sensor pad is 30milliseconds (ms) (e.g., to complete one scan). However, the minimumsample rate of PS/2 may be 10-12.5 ms. For example, in the stream modeof the PS/2 protocol, the user interface sends movement data when itdetects movement or a change in state of one or more buttons. Themaximum rate at which this data reporting may occur is known as thesample rate. This parameter ranges from 10 samples/sec to 200samples/sec. The default value for the sample rate is 100 samples/seeand the host may change that value. Conventional computers will set thesample rate to 80 samples/sec or 100 samples/sec, resulting in minimumsampling times of 12.5 ms and 10 ms, respectively. Accordingly, a userwill notice the position “jumps” in the cursor with scan speeds slowerthan the minimum sample rate. Further, the slower scan speed in thesample rate of the interface may bottleneck data communication betweenthe user interface device and the host.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings.

FIG. 1A illustrates a conventional touch-sensor pad.

FIG. 1B illustrates a graph of the capacitance over time of theconventional touch-sensor pad described above.

FIG. 2 illustrates a block diagram of one embodiment of an electronicsystem having a processing device for capacitive sensing.

FIG. 3A illustrates a varying switch capacitance.

FIG. 3B illustrates one embodiment of a relaxation oscillator.

FIG. 4 illustrates a block diagram of one embodiment of a capacitancesensor including a relaxation oscillator and digital counter.

FIG. 5A illustrates a top-side view of one embodiment of a sensor arrayhaving a plurality of sensor elements for detecting a presence of aconductive object on the sensor array of a touch-sensor pad.

FIG. 5B illustrates a top-side view of one embodiment of a sensor arrayhaving a plurality of sensor elements for detecting a presence of aconductive object on the sensor array of a touch-sensor slider

FIG. 5C illustrates a top-side view of one embodiment of a two-layertouch-sensor pad.

FIG. 5D illustrates a side view of one embodiment of the two-layertouch-sensor pad of FIG. 5C.

FIG. 6 illustrates a block diagram of one embodiment of a sensing deviceincluding a switch circuit.

FIG. 7A illustrates a block diagram of one exemplary embodiment ofswitch circuit.

FIG. 7B illustrates a block diagram of the switch circuit of FIG. 7A ina first setting.

FIG. 7C illustrates a block diagram of the switch circuit of FIG. 7A ina second setting.

FIG. 8A illustrates a block diagram of another exemplary embodiment of aswitch circuit.

FIG. 8B illustrates a block diagram of the switch circuit of FIG. 8A ina first selling.

FIG. 8C illustrates a block diagram of the switch circuit of FIG. 8A ina second setting.

FIG. 9A illustrates a block diagram of another exemplary embodiment of aswitch circuit.

FIG. 9B illustrates a block diagram of the switch circuit of FIG. 9A ina first setting.

FIG. 9C illustrates a block diagram of the switch circuit of FIG. 9A ina second setting.

FIG. 9D illustrates a block diagram of the switch circuit of FIG. 8A ina second setting.

DETAILED DESCRIPTION

Described herein is a method and apparatus for detecting the presence ofthe conductive object to determine a position of the conductive objectusing a first and second scans. The following description sets forthnumerous specific details such as examples of specific systems,components, methods, and so forth, in order to provide a goodunderstanding of several embodiments of the present invention. It willbe apparent to one skilled in the art, however, that at least someembodiments of the present invention may be practiced without thesespecific details. In other instances, well-known components or methodsare not described in detail or are presented in simple block diagramformat in order to avoid unnecessarily obscuring the present invention.Thus, the specific details set forth are merely exemplary. Particularimplementations may vary from these exemplary details and still becontemplated to be within the spirit and scope of the present invention.

Embodiments of a method and apparatus are described to determine aposition of a conductive object on a sensing device using first andsecond scans. In one embodiment, the method may include detecting apresence of a conductive object in a first area of a sensing deviceusing a first scan of the sensing device, wherein the first area is lessthan an entire area of the sensing device, and detecting the presence ofthe conductive object to determine a position of the conductive objectwithin the first area using a second scan of the first area of thesensing device. The first scan may include scanning two or more firstscan groups of sensor elements during the first scan, where each groupof sensor elements is separately scanned during the first scan. Eachgroup includes two or more sensor elements coupled together during thefirst scan. Also the first scan includes selecting a group of the two ormore first scan groups that includes the first area in which thepresence of the conductive object is detected. The second scan includesscanning two or more sensor elements of the selected group that includesthe first area during the second scan. Each sensor clement of the two ormore sensor elements is separately scanned during the second scan. Also,the second scan includes selecting a sensor clement of the two or moresensor elements of the selected group that includes the detectedpresence of the conductive object.

The apparatus may include a plurality of sensor elements to detect apresence of a conductive object on the sensing device, and a switchcircuit coupled to the plurality of sensor elements. The switch circuitis configured to group the plurality of sensor elements into multiplefirst scan groups and a second scan group. The apparatus may alsoinclude a processing device coupled to the switch circuit. Theprocessing device comprises one or more capacitance sensors coupled tothe switch circuit to measure capacitance on the plurality of sensorelements.

The switch circuit includes two settings. The first setting of theswitch circuit groups the n strips (e.g., sensor elements) into firstscan groups (e.g., coarse scan groups). The sensor elements of eachgroup are coupled together. By performing a coarse detection of thesensing device, one of the groups will be selected (e.g., for finescan). In the second setting, all the capacitance sensors, previouslycoupled to the groups of combined strips, will be switched to be coupledto the strips (e.g., sensor elements) in this selected group (e.g., finescan group). At this fine detecting phase, the exact strip (e.g., sensorelement) being touched is located.

With this new approach, it may take, in average, 2√{square root over(N)} cycles per scan, compared against (N+1)/2 cycles per scan withlinear search algorithm.

The switch circuit, described herein, may also be configured to groupthe sensor elements (e.g., strips or pads) in two settings. One settingis used for a coarse scan to detect a presence of a conductive object ina first area that is smaller than the entire area of the entire sensingdevice. The second setting is used for a fine scan to detect thepresence of the conductive object to determine a position of theconductive object within the first area detected in the first setting.The first setting is used during the first scan, and the second settingis used for the second scan. Using switch circuit to group the sensorelements at coarse and fine phase to elevate the scan rate to theperformance level of binary search algorithm.

FIG. 2 illustrates a block diagram of one embodiment of an electronicsystem having a processing device for recognizing a tap gesture.Electronic system 200 includes processing device 210, touch-sensor pad220, touch-sensor 230, touch-sensor buttons 240, host processor 250,embedded controller 260, and non-capacitance sensor elements 270. Theprocessing device 210 may include analog and/or digital general purposeinput/output (“GPIO”) ports 207. GPIO ports 207 may be programmable.GPIO ports 207 may be coupled to a Programmable Interconnect and Logic(“PIL”), which acts as an interconnect between GPIO ports 207 and adigital block array of the processing device 210 (not illustrated). Thedigital block array may be configured to implement a variety of digitallogic circuits (e.g., DAC, digital filters, digital control systems,etc.) using, in one embodiment, configurable user modules (“UMs”). Thedigital block array may be coupled to a system bus. Processing device210 may also include memory, such as random access memory (RAM) 205 andprogram flash 204. RAM 205 may be static RAM (SRAM), and program flash204 may be a non-volatile storage, which may be used to store firmware(e.g., control algorithms executable by processing core 202 to implementoperations described herein). Processing device 210 may also include amemory controller unit (MCU) 203 coupled to memory and the processingcore 202.

The processing device 210 may also include an analog block array (notillustrated). The analog block array is also coupled to the system bus.Analog block array also may be configured to implement a variety ofanalog circuits (e.g., ADC, analog filters, etc.) using configurableUMs. The analog block array may also be coupled to the GPIO 207.

As illustrated, capacitance sensor 201 may be integrated into processingdevice 210. Capacitance sensor 201 may include analog I/O for couplingto an external component, such as touch-sensor pad 220, touch-sensorslider 230, touch-sensor buttons 240, and/or other devices. Capacitancesensor 201 and processing device 202 are described in more detail below.

It should be noted that the embodiments described herein are not limitedto touch-sensor pads for notebook implementations, but can be used inother capacitive sensing implementations, for example, the sensingdevice may be a touch-slider 230, or a touch-sensor 240 (e.g.,capacitance sensing button). Similarly, the operations described hereinare not limited to notebook cursor operations, but can include otheroperations, such as lighting control (dimmer), volume control, graphicequalizer control, speed control, or other control operations requiringgradual adjustments. It should also be noted that these embodiments ofcapacitive sensing implementations may be used in conjunction withnon-capacitive sensing elements, including but not limited to pickbuttons, sliders (ex. display brightness and contrast), scroll-wheels,multi-media control (ex. volume, track advance, etc) handwritingrecognition and numeric keypad operation.

In one embodiment, the electronic system 200 includes a touch-sensor pad220 coupled to the processing device 210 via bus 221. Touch-sensor pad220 may include a multi-dimension sensor array. The mold-dimensionsensor array comprises a plurality of sensor elements, organized as rowsand columns. In another embodiment, the electronic system 200 includes atouch-sensor slider 230 coupled to the processing device 210 via bus231. Touch-sensor slider 230 may include a single-dimension sensorarray. The single-dimension sensor array comprises a plurality of sensorelements, organized as rows, or alternatively, as columns. In anotherembodiment, the electronic system 200 includes a touch-sensor button 240coupled to the processing device 210 via bus 241. Touch-sensor button240 may include a single-dimension or multi-dimension sensor array. Thesingle- or multi-dimension sensor array comprises a plurality of sensorelements. For a touch-sensor button, the plurality of sensor elementsmay be coupled together to detect a presence of a conductive object overthe entire surface of the sensing device. Capacitance sensor elementsmay be used as non-contact switches. These switches, when protected byan insulating layer, offer resistance to severe environments.

The electronic system 200 may include any combination of one or more ofthe touch-sensor pad 220, touch-sensor slider 230, and/or touch-sensorbutton 240. In another embodiment, the electronic system 200 may alsoinclude non-capacitance sensor elements 270 coupled to the processingdevice 210 via bus 271. The non-capacitance sensor elements 270 mayinclude buttons, light emitting diodes (LEDs), and other user interfacedevices, such as a mouse, a keyboard, or other functional keys that donot require capacitance sensing. In one embodiment, buses 271, 241, 231,and 221 may be a single bus. Alternatively, these buses may beconfigured into any combination of one or more separate buses.

The processing device may also provide value-add functionality such askeyboard control integration, LEDs, battery charger and general purposeI/O, as illustrated as non-capacitance sensor elements 270.Non-capacitance sensor elements 270 are coupled to the GPIO 207.

Processing device 210 may include internal oscillator/clocks 206, andcommunication block 208. The oscillator/clocks block 206 provides clocksignals to one or more of the components of processing device 210.Communication block 208 may be used to communicate with an externalcomponent, such as a host processor 250, via host interface (I/F) line251. Alternatively, processing block 210 may also be coupled to embeddedcontroller 260 to communicate with the external components, such as host250. Interfacing to the host 205 can be through various methods. In oneexemplary embodiment, interfacing with the host 250 may be done using astandard PS/2 interface to connect to an embedded controller 260, whichin turn sends data to the host 250 via low pin count (LPC) interface. Insome instances, it may be beneficial for the processing device 210 to doboth touch-sensor pad and keyboard control operations, thereby freeingup the embedded controller 260 for other housekeeping functions. Inanother exemplary embodiment, interfacing may be done using a universalserial bus (USB) interface directly coupled to the host 250 via hostinterface line 251. Alternatively, the processing device 210 maycommunicate to external components, such as the host 250 using industrystandard interfaces, such as USB, PS/2, inter-integrated circuit (I2C)bus, or system packet interface (SPI). The embedded controller 260and/or embedded controller 260 may be coupled to the processing device210 with a ribbon or flex cable from an assembly, which houses thetouch-sensor pad and processing device.

In one embodiment, the processing device 210 is configured tocommunicate with the embedded controller 260 or the host 250 to senddata. The data may be a command or alternatively a signal. In anexemplary embodiment, the electronic system 200 may operate in bothstandard-mouse compatible and enhanced modes. The standard-mousecompatible mode utilizes the HID class drivers already built into theOperating System (OS) software of host 250. These drivers enable theprocessing device 210 and sensing device to operate as a standard cursorcontrol user interface device, such as a two-button PS/2 mouse. Theenhanced mode may enable additional features such as scrolling(reporting absolute position) or disabling the sensing device, such aswhen a mouse is plugged into the notebook. Alternatively, the processingdevice 210 may be configured to communicate with the embedded controller260 or the host 250 using non-OS drivers, such as dedicated touch-sensorpad drivers, or other drivers known by those of ordinary skill in theart.

In other words, the processing device 210 may operate to communicatedata (e.g., via commands or signals) using hardware, software, and/orfirmware, and the data may be communicated directly to the processingdevice of the host 250, such as a host processor, or alternatively, maybe communicated to the host 250 via drivers of the host 250, such as OSdrivers, or other non-OS drivers. It should also be noted that the host250 may directly communicate with the processing device 210 via hostinterface 251.

In one embodiment, the data sent to the host 250 from the processingdevice 210 includes click, double-click, movement of the cursor,scroll-up, scroll-down, scroll-left, scroll-right, step Back, and stepForward. Alternatively, other user interface device commands maybecommunicated to the host 250 from the processing device 210. Thesecommands may be based on gestures occurring on the sensing device thatare recognized by the processing device, such as tap, push, hop, andzigzag gestures. Alternatively, other commands may be recognized.Similarly, signals may be sent that indicate the recognition of theseoperations.

In particular, a tap gesture, for example, may be when the finger (e.g.,conductive object) is on the sensing device for less than a thresholdtime. If the time the finger is placed on the touchpad is greater thanthe threshold time it may be considered to be a movement of the cursor,in the x- or y-axes. Scroll-up, scroll-down, scroll-left, andscroll-right, step back, and step-forward may be detected when theabsolute position of the conductive object is within a pre-defined area,and movement of the conductive object is detected.

Processing device 210 may reside on a common carrier substrate such as,for example, an integrated circuit (IC) die substrate, a multi-chipmodule substrate, or the like. Alternatively, the components ofprocessing device 210 may be one or more separate integrated circuitsand/or discrete components. In one exemplary embodiment, processingdevice 210 may be a Programmable System on a Chip (PSoC™) processingdevice, manufactured by Cypress Semiconductor Corporation, San Jose,Calif. Alternatively, processing device 210 may be other one or moreprocessing devices known by those of ordinary skill in the art, such asa microprocessor or central processing unit, a controller,special-purpose processor, digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), or the like. In an alternative embodiment, forexample, the processing device may be a network processor havingmultiple processors including a core unit and multiple microengines.Additionally, the processing device may include any combination ofgeneral-purpose processing device(s) and special-purpose processingdevice(s).

Capacitance sensor 201 may be integrated into the IC of the processingdevice 210, or alternatively, in a separate IC. Alternatively,descriptions of capacitance sensor 201 may be generated and compiled forincorporation into other integrated circuits. For example, behaviorallevel code describing capacitance sensor 201, or portions thereof, maybe generated using a hardware descriptive language, such as VHDL orVerilog, and stored to a machine-accessible medium (e.g., CD-ROM, harddisk, floppy disk, etc.). Furthermore, the behavioral level code can becompiled into register transfer level (“RTL”) code, a netlist, or even acircuit layout and stored to a machine-accessible medium. The behaviorallevel code, the RTL code, the netlist, and the circuit layout allrepresent various levels of abstraction to describe capacitance sensor201.

It should be noted that the components of electronic system 200 mayinclude all the components described above. Alternatively, electronicsystem 200 may include only some of the components described above.

In one embodiment, electronic system 200 may be used in a notebookcomputer. Alternatively, the electronic device may be used in otherapplications, such as a mobile handset, a personal data assistant (PDA),a keyboard, a television, a remote control, a monitor, a handheldmulti-media device, a handheld video player, a handheld gaming device,or a control panel.

In one embodiment, capacitance sensor 201 may be a capacitive switchrelaxation oscillator (CSR). The CSR may have an array of capacitivetouch switches using a current-programmable relaxation oscillator, ananalog multiplexer, digital counting functions, and high-level softwareroutines to compensate for environmental and physical switch variations.The switch array may include combinations of independent switches,sliding switches (e.g., touch-sensor slider), and touch-sensor padsimplemented as a pair of orthogonal sliding switches. The CSR mayinclude physical, electrical, and software components. The physicalcomponent may include the physical switch itself, typically a patternconstructed on a printed circuit hoard (PCB) with an insulating cover, aflexible membrane, or a transparent overlay. The electrical componentmay include an oscillator or other means to convert a changedcapacitance into a measured signal. The electrical component may alsoinclude a counter or timer to measure the oscillator output. Thesoftware component may include detection and compensation softwarealgorithms to convert the count value into a switch detection decision.For example, in the case of slide switches or X-Y touch-sensor pads, acalculation for finding position of the conductive object to greaterresolution than the physical pitch of the switches may be used.

It should be noted that there are various known methods for measuringcapacitance. Although the embodiments described herein are describedusing a relaxation oscillator, the present embodiments are not limitedto using relaxation oscillators, but may include other methods, such ascurrent versus voltage phase shift measurement, resistor-capacitorcharge timing, capacitive bridge divider or, charge transfer.

The current versus voltage phase shift measurement may include drivingthe capacitance through a fixed-value resistor to yield voltage andcurrent waveforms that are out of phase by a predictable amount. Thedrive frequency can be adjusted to keep the phase measurement in areadily measured range. The resistor-capacitor charge timing may includecharging the capacitor through a fixed resistor and measuring timing onthe voltage ramp. Small capacitor values may require very largeresistors for reasonable timing. The capacitive bridge divider mayinclude driving the capacitor under test through a fixed referencecapacitor. The reference capacitor and the capacitor under test form avoltage divider. The voltage signal is recovered with a synchronousdemodulator, which may be done in the processing device 210. The chargetransfer may be conceptually similar to an R-C charging circuit. In thismethod, C_(P) is the capacitance being sensed. C_(SUM) is the summingcapacitor, into which charge is transferred on successive cycles. At thestart of the measurement cycle, the voltage on C_(SUM) is reset. Thevoltage on C_(SUM) increases exponentially (and only slightly) with eachclock cycle. The time for this voltage to reach a specific threshold ismeasured with a counter. Additional details regarding these alternativeembodiments have not been included so as to not obscure the presentembodiments, and because these alternative embodiments for measuringcapacitance are known by those of ordinary skill in the art.

FIG. 3A illustrates a varying switch capacitance. In its basic form, acapacitive switch 300 is a pair of adjacent plates 301 and 302. There isa small edge-to-edge capacitance Cp, but the intent of switch layout isto minimize the base capacitance Cp between these plates. When aconductive object 303 (e.g., finger) is placed in proximity to the twoplate 301 and 302, there is a capacitance 2*Cf between one electrode 301and the conductive object 303 and a similar capacitance 2*Cf between theconductive object 303 and the other electrode 302. The capacitancebetween one electrode 301 and the conductive object 303 and hack to theother electrode 302 adds in parallel to the base capacitance Cp betweenthe plates 301 and 302, resulting in a change of capacitance Cf.Capacitive switch 300 may be used in a capacitance switch array. Thecapacitance switch array is a set of capacitors where one side of eachis grounded. Thus, the active capacitor (as represented in FIG. 3B ascapacitor 351) has only one accessible side. The presence of theconductive object 303 increases the capacitance (Cp+Cf) of the switch300 to ground. Determining switch activation is then a matter ofmeasuring change in the capacitance (Cf). Switch 300 is also known as agrounded variable capacitor. In one exemplary embodiment, Cf may rangefrom approximately 10-30 picofarads (pF). Alternatively, other rangesmay be used.

The conductive object in this case is a finger, alternatively, thistechnique may be applied to any conductive object, for example, aconductive door switch, position sensor, or conductive pen in a stylustracking system.

FIG. 3B illustrates one embodiment of a relaxation oscillator. Therelaxation oscillator 350 is formed by the capacitance to be measured oncapacitor 351, a charging current source 352, a comparator 353, and areset switch 354. It should be noted that capacitor 351 isrepresentative of the capacitance measured on a sensor element of asensor array. The relaxation oscillator is coupled to drive a chargingcurrent (Ic) 357 in a single direction onto a device under test (“DUT”)capacitor, capacitor 351. As the charging current piles charge onto thecapacitor 351, the voltage across the capacitor increases with time as afunction of Ic 357 and its capacitance C. Equation (1) describes therelation between current, capacitance, voltage and time for a chargingcapacitor.

CdV=I_(C)dt   (1)

The relaxation oscillator begins by charging the capacitor 351 from aground potential or zero voltage and continues to pile charge on thecapacitor 351 at a fixed charging current Ic 357 until the voltageacross the capacitor 351 at node 355 reaches a reference voltage orthreshold voltage, V_(TH) 355. At V_(TH) 355, the relaxation oscillatorallows the accumulated charge at node 355 to discharge (e.g., thecapacitor 351 to “relax” hack to the ground potential) and then theprocess repeats itself. In particular, the output of comparator 353asserts a clock signal F_(OUT) 356 (e.g., F_(OUT) 356 goes high), whichenables the reset switch 354. This resets the voltage on the capacitorat node 355 to ground and the charge cycle starts again. The relaxationoscillator outputs a relaxation oscillator clock signal (F_(OUT) 356)having a frequency (f_(RO)) dependent upon capacitance C of thecapacitor 351 and charging current Ic 357.

The comparator trip time of the comparator 353 and reset switch 354 adda fixed delay. The output of the comparator 353 is synchronized with areference system clock to guarantee that the comparator reset time islong enough to completely reset the charging voltage on capacitor 355.This sets a practical upper limit to the operating frequency. Forexample, if capacitance C of the capacitor 351 changes, then f_(RO) willchange proportionally according to Equation (1). By comparing f_(RO) off_(OUT) 356 against the frequency (f_(REF)) of a known reference systemclock signal (REF CLK) the change in capacitance ΔC can be measured.Accordingly, equations (2) and (3) below describe that a change infrequency between F_(OUT) 356 and REF CLK is proportional to a change incapacitance of the capacitor 351.

ΔC∝Δf, where   (2)

Δf=f _(RO) −f _(REF).   (3)

In one embodiment, a frequency comparator may be coupled to receiverelaxation oscillator clock signal (F_(OUT) 356) and REF CLK, comparetheir frequencies f_(RO) and f_(REF), respectively, and output a signalindicative of the difference Δf between these frequencies. By monitoringΔf one can determine whether the capacitance of the capacitor 351 haschanged.

In one exemplary embodiment, the relaxation oscillator 350 may be builtusing a 555 timer to implement the comparator 353 and reset switch 354.Alternatively, the relaxation oscillator 350 may be built using othercircuiting. Relaxation oscillators are known in by those of ordinaryskill m the art, and accordingly, additional details regarding theiroperation have not been included so as to not obscure the presentembodiments.

FIG. 4 illustrates a block diagram of one embodiment of a capacitancesensor including a relaxation oscillator and digital counter.Capacitance sensor 201 of FIG. 4 includes a sensor array 410 (also knownas a switch array), relaxation oscillator 350, and a digital counter420. Sensor array 410 includes a plurality of sensor elements355(1)-355(N), where N is a positive integer value that represents thenumber of rows (or alternatively columns) of the sensor array 410. Eachsensor element is represented as a capacitor, as previously describedwith respect to FIG. 3B. The sensor array 410 is coupled to relaxationoscillator 350 via an analog bus 401 having a plurality of pins401(1)-401(N). In one embodiment, the sensor array 410 may be asingle-dimension sensor array including the sensor elements355(1)-355(N), where N is a positive integer Value that represents thenumber of sensor elements of the single-dimension sensor array. Thesingle-dimension sensor array 410 provides output data to the analog bus401 of the processing device 210 (e.g., via lines 231). Alternatively,the sensor array 410 may be a multi-dimension sensor array including thesensor elements 355(1)-355(N), where N is a positive integer value thatrepresents the number of sensor elements of the multi-dimension sensorarray. The multi-dimension sensor array 410 provides output data to theanalog bus 401 of the processing device 210 (e.g., via bus 221).

Relaxation oscillator 350 of FIG. 4 includes all the componentsdescribed with respect to FIG. 3B, and a selection circuit 430. Theselection circuit 430 is coupled to the plurality of sensor elements355(1)-355(N), the reset switch 354, the current source 352, and thecomparator 353. Selection circuit 430 may be used to allow therelaxation oscillator 350 to measure capacitance on multiple sensorelements (e.g., rows or columns). The selection circuit 430 may beconfigured to sequentially select a sensor element of the plurality ofsensor elements to provide the charge current and to measure thecapacitance of each sensor element. In one exemplary embodiment, theselection circuit 430 is a multiplexer array of the relaxationoscillator 350. Alternatively, selection circuit may be other circuitryoutside the relaxation oscillator 350, or even outside the capacitancesensor 201 to select the sensor clement to be measured. Capacitancesensor 201 may include one relaxation oscillator and digital counter forthe plurality of sensor elements of the sensor array. Alternatively,capacitance sensor 201 may include multiple relaxation oscillators anddigital counters to measure capacitance on the plurality of sensorelements of the sensor array. The multiplexer array may also be used toground the sensor elements that are not being measured. This may be donein conjunction with a dedicated pin in the GP10 port 207.

In another embodiment, the capacitance sensor 201 may be configured tosimultaneously scan the sensor elements, as opposed to being configuredto sequentially scan the sensor elements as described above. Forexample, the sensing device may include a sensor array having aplurality of rows and columns. The rows may be scanned simultaneously,and the columns may be scanned simultaneously.

In one exemplary embodiment, the voltages on all of the rows of thesensor array are simultaneously moved, while the voltages of the columnsare held at a constant voltage, with the complete set of sampled pointssimultaneously giving a profile of the conductive object in a firstdimension. Next, the voltages on all of the rows are held at a constantvoltage, while the voltages on all the rows are simultaneously moved, toobtain a complete set of sampled points simultaneously giving a profileof the conductive object in the other dimension.

In another exemplary embodiment, the voltages on all of the rows of thesensor array are simultaneously moved in a positive direction, while thevoltages of the columns are moved in a negative direction. Next, thevoltages on all of the rows of the sensor array are simultaneously movedin a negative direction, while the voltages of the columns are moved ina positive direction. This technique doubles the effect of anytranscapacitance between the two dimensions, or conversely, halves theeffect of any parasitic capacitance to the ground. In both methods, thecapacitive information from the sensing process provides a profile ofthe presence of the conductive object to the sensing device in eachdimension. Alternatively, other methods for scanning known by those ofordinary skill in the art may be used to scan the sensing device.

Digital counter 420 is coupled to the output of the relaxationoscillator 350. Digital counter 420 receives the relaxation oscillatoroutput signal 356 (F_(OUT)). Digital counter 420 is configured to countat least one of a frequency or a period of the relaxation oscillatoroutput received from the relaxation oscillator.

As previously described with respect to the relaxation oscillator 350,when a finger or conductive object is placed on the switch, thecapacitance increases from Cp to Cp+Cf so the relaxation oscillatoroutput signal 356 (F_(OUT)) decreases. The relaxation oscillator outputsignal 356 (F_(OUT)) is fed to the digital counter 420 for measurement.There are two methods for counting the relaxation oscillator outputsignal 356, frequency measurement and period measurement. In oneembodiment, the digital counter 420 may include two multiplexers 423 and424. Multiplexers 423 and 424 are configured to select the inputs forthe PWM 421 and the timer 422 for the two measurement methods, frequencyand period measurement methods. Alternatively, other selection circuitsmay be used to select the inputs for the PWM 421 and the time 422. Inanother embodiment, multiplexers 423 and 424 are not included in thedigital counter, for example, the digital counter 420 may be configuredin one, or the other, measurement configuration.

In the frequency measurement method, the relaxation oscillator outputsignal 356 is counted for a fixed period of time. The counter 422 isread to obtain the number of counts during the gate time. This methodworks well at low frequencies where the oscillator reset time is smallcompared to the oscillator period. A pulse width modulator (PWM) 441 isclocked for a fixed period by a derivative of the system clock, VC3 426(which is a divider from the 24 MHz system clock 425). Pulse widthmodulation is a modulation technique that generates variable-lengthpulses to represent the amplitude of an analog input signal; in thiscase VC3 426. The output of PWM 421 enables timer 422 (e.g., 16-bit).The relaxation oscillator output signal 356 clocks the timer 422. Thetimer 422 is reset at the start of the sequence, and the count value isread out at the end of the gate period.

In the period measurement method, the relaxation oscillator outputsignal 356 gates a counter 422, which is clocked by the system clock 425(e.g., 24 MHz). In order to improve sensitivity and resolution, multipleperiods of the oscillator are counted with the PWM 421. The output ofPWM 421 is used to gate the timer 422. In this method, the relaxationoscillator output signal 356 drives the clock input of PWM 421. Aspreviously described, pulse width modulation is a modulation techniquethat generates variable-length pulses to represent the amplitude of ananalog input signal in this case the relaxation oscillator output signal356. The output of the PWM 421 enables a timer 422 (e.g., 16-bit), whichis clocked at the system clock frequency 425 (e.g., 24 MHz). When theoutput of PWM 421 is asserted (e.g., goes high), the count starts byreleasing the capture control. When the terminal count of the PWM 421 isreached, the capture signal is asserted (e.g., goes high), stopping thecount and setting the PWM's interrupt. The timer value is read in thisinterrupt. The relaxation oscillator 350 is indexed to the next switch(e.g., capacitor 351(2)) to be measured and the count sequence isstarted again.

The two counting methods may have equivalent performance in sensitivityand signal-to-noise ratio (SNR). The period measurement method may havea slightly faster data acquisition rate, but this rate is dependent onsoftware load and the values of the switch capacitances. The frequencymeasurement method has a fixed-switch data acquisition rate.

The length of the counter 422 and the detection time required for theswitch are determined by sensitivity requirements. Small changes in thecapacitance on capacitor 351 result in small changes in frequency. Inorder to find these small changes, it may be necessary to count for aconsiderable time.

At startup (or boot) the switches (e.g., capacitors 351(1)-(N)) arescanned and the count values for each switch with no actuation arestored as a baseline array (Cp). The presence of a finger on the switchis determined by the difference in counts between a stored value for noswitch actuation and the acquired value with switch actuation, referredto here as Δn. The sensitivity of a single switch is approximately:

$\begin{matrix}{\frac{\Delta \; n}{n} = \frac{Cf}{Cp}} & (4)\end{matrix}$

The value of Δn should be large enough for reasonable resolution andclear indication of switch actuation. This drives switch constructiondecisions.

Cf should be as large a fraction of Cp as possible. In one exemplaryembodiment, the fraction of Cf/Cp ranges between approximately 0.01 toapproximately 2.0. Alternatively, other fractions may be used for Cf/Cp.Since Cf is determined by finger area and distance from the finger tothe switch's conductive traces (through the over-lying insulator), thebaseline capacitance Cp should be minimized. The baseline capacitance Cpincludes the capacitance of the switch pad plus any parasitics,including routing and chip pin capacitance.

In switch array applications, variations in sensitivity should be minitrued. If there are large differences in Δn, one switch may actuate at1.0 cm, while another may not actuate until direct contact. Thispresents a non-ideal user interface device. There are numerous methodsfor balancing the sensitivity. These may include precisely matchingon-board capacitance with PC trace length modification, adding balancecapacitors on each switch's PC board trace, and/or adapting acalibration factor to each switch to be applied each time the switch istested.

In one embodiment, the PCB design may be adapted to minimizecapacitance, including thicker PCBs where possible. In one exemplaryembodiment, a 0.062 inch thick PCB is used. Alternatively, otherthicknesses may be used, for example, a 0.015 inch thick PCB.

It should be noted that the count window should be long enough for Δn tobe a “significant number.” In one embodiment, the “significant number”can be as little as 10, or alternatively, as much as several hundred. Inone exemplary embodiment, where Cf is 1.0% of Cp (a typical “weak”switch), and where the switch threshold is set at a count value of 20, nis found to be:

$\begin{matrix}{n = {{\Delta \; {n \cdot \frac{Cf}{Cp}}} = 2000}} & (5)\end{matrix}$

Adding some margin to yield 2500 counts, and running the frequencymeasurement method at 1.0 MHz, the detection time for the switch is 4microseconds. In the frequency measurement method, the frequencydifference between a switch with and without actuation (i.e., CP+CF vs.CP) is approximately:

$\begin{matrix}{{\Delta \; n} = {\frac{t_{count} \cdot i_{c}}{V_{TH}}\frac{Cf}{{Cp}^{2}}}} & (6)\end{matrix}$

This shows that the sensitivity variation between one channel andanother is a function of the square of the difference in the twochannels' static capacitances. This sensitivity difference can becompensated using routines in the high-level Application ProgrammingInterfaces (APIs).

In the period measurement method, the count difference between a switchwith and without actuation (i.e., CP+CF vs. CP) is approximately:

$\begin{matrix}{{\Delta \; n} = {N_{Periods} \cdot \frac{{Cf} \cdot V_{TH}}{i_{C}} \cdot f_{SysClk}}} & (7)\end{matrix}$

The charge currents are typically lower and the period is longer toincrease sensitivity, or the number of periods for which f_(SysClk) iscounted can be increased. In either method, by matching the static(parasitic) capacitances Cp of the individual switches, therepeatability of detection increases, making all switches work at thesame difference. Compensation for this variation can be done in softwareat runtime. The compensation algorithms for both the frequency methodand period method may be included in the high-level APIs.

Some implementations of this circuit use a current source programmed bya fixed-resistor value. If the range of capacitance to be measuredchanges, external components, (i.e., the resistor) should be adjusted.

Using the multiplexer array 430, multiple sensor elements may besequentially scanned to provide current to and measure the capacitancefrom the capacitors (e.g., sensor elements), as previously described. Inother words, while one sensor element is being measured, the remainingsensor elements are grounded using the GPIO port 207. This drive andmultiplex arrangement bypasses the existing GPIO to connect the selectedpin to an internal analog multiplexer (mux) bus. The capacitor chargingcurrent (e.g., current source 352) and reset switch 353 are connected tothe analog mux bus. This may limit the pin-count requirement to simplythe number of switches (e.g., capacitors 351(1)-351(N)) to be addressed.In one exemplary embodiment, no external resistors or capacitors arerequired inside or outside the processing device 210 to enableoperation.

The capacitor charging current for the relaxation oscillator 350 isgene-rated in a register programmable current output DAC (also known asIDAC). Accordingly, the current source 352 is a current DAC or IDAC. TheIDAC output current may be set by an 8-bit value provided by theprocessing device 210, such as from the processing core 202. The 8-bitvalue may be stored in a register or in memory.

Estimating and measuring PCB capacitances may be difficult; theoscillator-reset time may add to the oscillator period (especially athigher frequencies); and there may be some variation to the magnitude ofthe MAC output current with operating frequency. Accordingly, theoptimum oscillation frequency and operating current for a particularswitch array may be determined to some degree by experimentation.

In many capacitive switch designs the two “plates” (e.g., 301 and 302)of the sensing capacitor are actually adjacent PCB pads or traces, asindicated in FIG. 3A. Typically, one of these plates is grounded.Layouts for touch-sensor slider (e.g., linear slide switches) andtouch-sensor pad applications have switches that are immediatelyadjacent. In this case, all of the switches that are not active aregrounded through the GPIO 207 of the processing device 210 dedicated tothat pin. The actual capacitance between adjacent plates is small (Cp),but the capacitance of the active plate (and its PCB trace back to theprocessing device 210) to ground, when detecting the presence of theconductive object 303, may be considerably higher (Cp+Cf). Thecapacitance of two parallel plates is given by the following equation:

$\begin{matrix}{C = {{ɛ_{0} \cdot ɛ_{R} \cdot \frac{A}{d}} = {{ɛ_{R} \cdot 8.85 \cdot \frac{A}{d}}{pF}\text{/}m}}} & (8)\end{matrix}$

The dimensions of equation (8) are in meters. This is a very simplemodel of the capacitance. The reality is that there are fringing effectsthat substantially increase the switch-to-ground (and PCBtrace-to-ground) capacitance.

Switch sensitivity (i.e., actuation distance) may be increased by one ormore of the following: 1) increasing board thickness to increase thedistance between the active switch and any parasitics; 2) minimizing PCtrace routing underneath switches; 3) utilizing a glided ground with 50%or less fill if use of a ground plane is absolutely necessary; 4)increasing the spacing between switch pads and any adjacent groundplane; 5) increasing pad area; 6) decreasing thickness of any insulatingoverlay; or 7) verifying that there is no air-gap between the PC padsurface and the touching finger.

There is some variation of switch sensitivity as a result ofenvironmental factors. A baseline update routine, which compensates forthis variation, may be provided in the high-level APIs.

Sliding switches are used for control requiring gradual adjustments.Examples include a lighting control (dimmer), volume control, graphicequalizer, and speed control. These switches are mechanically adjacentto one another. Actuation of one switch results in partial actuation ofphysically adjacent switches. The actual position in the sliding switchis found by computing the centroid location of the set of switchesactivated.

In applications for touch-sensor sliders (e.g., sliding switches) andtouch-sensor pads it is often necessary to determine finger for othercapacitive object) position to more resolution than the native pitch ofthe individual switches. The contact area of a finger on a slidingswitch or a touch pad is often larger than any single switch. In oneembodiment, in order to calculate the interpolated position using acentroid, the array is first scanned to verify that a given switchlocation is valid. The requirement is for some number of adjacent switchsignals to be above a noise threshold. When the strongest signal isfound, this signal and those immediately adjacent are used to compute acentroid:

$\begin{matrix}{{Centroid} = \frac{{n_{i - 1} \cdot \left( {i - 1} \right)} + {n_{i}i} + {n_{i + 1} \cdot \left( {i + 1} \right)}}{n_{i - 1} + {n_{i}i} + n_{i + 1}}} & (9)\end{matrix}$

The calculated value will almost certainly be fractional. In order toreport the centroid to a specific resolution, for example a range of 0to 100 for 12 switches, the centroid value may be multiplied by acalculated scalar. It may be more efficient to combine the interpolationand scaling operations into a single calculation and report this resultdirectly in the desired scale. This may be handled in the high-levelAPIs. Alternatively, other methods may be used to interpolate theposition of the conductive object.

A physical touchpad assembly is a multi-layered module to detect aconductive object. In one embodiment, the multi-layer stack-up of atouchpad assembly includes a PCB, an adhesive layer, and an overlay. ThePCB includes the processing device 210 and other components, such as theconnector to the host 250, necessary for operations for sensing thecapacitance. These components are on the non-sensing side of the PCB.The PCB also includes the sensor array on the opposite side, the sensingside of the PCB. Alternatively, other multi-layer stack-ups may be usedin the touchpad assembly.

The PCB may be made of standard materials, such as FR4 or Kapton™ (e.g.,flexible PCB). In either case, the processing device 210 may be attachedsoldered) directly to the sensing PCB (e.g., attached to the non-sensingside of the PCB). The PCB thickness varies depending on multiplevariables, including height restrictions and sensitivity requirements.In one embodiment, the PCB thickness is at least approximately 0.3millimeters (mm). Alternatively, the PCB may have other thicknesses. Itshould be noted that thicker PCBs may yield better results. The PCBlength and width is dependent on individual design requirements for thedevice on which the sensing device is mounted, such as a notebook ormobile handset.

The adhesive layer is directly on top of the PCB sensing array and isused to affix the overlay to the overall touchpad assembly. Typicalmaterial used for connecting the overlay to the PCB is non-conductiveadhesive such as 3M 467 or 468. In one exemplary embodiment, theadhesive thickness is approximately 0.05 mm. Alternatively, otherthicknesses may be used.

The overlay may be non-conductive material used to protect the PCBcircuitry to environmental elements and to insulate the user's finger(e.g., conductive object) from the circuitry. Overlay can be ABSplastic, polycarbonate, glass, or Mylar™ Alternatively, other materialsknown by those of ordinary skill in the art may be used. In oneexemplary embodiment, the overlay has a thickness of approximately 1.0mm. In another exemplary embodiment, the overlay thickness has athickness of approximately 2.0 mm. Alternatively, other thicknesses maybe used.

The sensor array may be a grid-like pattern of sensor elements (e.g.,capacitive elements) used in conjunction with the processing device 210to detect a presence of a conductive object, such as finger, to aresolution greater than that which is native. The touch-sensor padlayout pattern maximizes the area covered by conductive material, suchas copper, in relation to spaces necessary to define the rows andcolumns of the sensor array.

FIG. 5A illustrates a top-side view of one embodiment of a sensor arrayhaving a plurality of sensor elements for detecting a presence of aconductive object 303 on the sensor array 500 of a touch-sensor pad.Touch-sensor pad 220 includes a sensor array 500. Sensor array 500includes a plurality of rows 504(1)-504(N) and a plurality of columns505(1)-505(M), where N is a positive integer value representative of thenumber of rows and M is a positive integer value representative of thenumber of columns. Each row includes a plurality of sensor elements503(1)-503(K), where K is a positive integer value representative of thenumber of sensor elements in the row. Each column includes a pluralityof sensor elements 501(1)-501(L), where L is a positive integer valuerepresentative of the number of sensor elements in the column.Accordingly, sensor array is an N×M sensor matrix. The N×M sensormatrix, in conjunction with the processing device 210, is configured todetect a position of a presence of the conductive object 303 in the x-,and y-directions.

FIG. 5B illustrates a top-side view of one embodiment of a sensor arrayhaving a plurality of sensor elements for detecting a presence of aconductive object 303 on the sensor array 550 of a touch-sensor slider.Touch-sensor slider 230 includes a sensor array 550. Sensor array 550includes a plurality of columns 504(1)-504(M), where M is a positiveinteger value representative of the number of columns. Each columnincludes a plurality of sensor elements 501(1)-501(L), where L is apositive integer value representative of the number of sensor elementsin the column. Accordingly, sensor array is a 1×M sensor matrix. The 1×Msensor matrix, in conjunction with the processing device 210, isconfigured to detect a position of a presence of the conductive object3t)3 in the x-direction. It should be noted that sensor array 500 may beconfigured to function as a touch-sensor slider 230.

Alternating columns in FIG. 5A correspond to x- and y-axis elements. They-axis sensor elements 503(1)-503(K) are illustrated as black diamondsin FIG. 5A, and the x-axis sensor dements 501(1)-501(L) are illustratedas white diamonds in FIG. 5A and FIG. 5B. It should be noted that othershapes may be used for the sensor elements. In another embodiment, thecolumns and row may include vertical and horizontal bars (e.g.,rectangular shaped bars), however, this design may include additionallayers in the PCB to allow the vertical and horizontal bars to bepositioned on the PCB so that they are not in contact with one another.

FIGS. 5C and 5D illustrate top-side and side views of one embodiment ofa two-layer touch-sensor pad. Touch-sensor pad, as illustrated in FIGS.5C and 5D, include the first two columns 505(1) and 505(2), and thefirst four rows 504(1)-504(4) of sensor array 500. The sensor elementsof the first column 501(1) are connected together in the top conductivelayer 575, illustrated as hashed diamond sensor elements andconnections. The diamond sensor elements of each column, in effect, forma chain of elements. The sensor elements of the second column 501(2) aresimilarly connected in the top conductive layer 575. The sensor elementsof the first row 504(1) are connected together in the bottom conductivelayer 575 using vias 577, illustrated as black diamond sensor elementsand connections. The diamond sensor elements of each row, in effect,form a chain of elements. The sensor elements of the second, third, andfourth rows 504(2)-504(4) are similarly connected in the bottomconductive layer 576.

As illustrated in FIG. 5D, the top conductive layer 575 includes thesensor elements for both the columns and the rows of the sensor array,as well as the connections between the senor elements of the columns ofthe sensor array. The bottom conductive layer 576 includes theconductive paths that connect the sensor elements of the rows thatreside in the top conductive layer 575. The conductive paths between thesensor elements of the rows use vias 577 to connect to one another inthe bottom conductive layer 576. Vias 577 go from the top conductivelayer 575, through the dielectric layer 578, to the bottom conductivelayer 576. Coating layers 579 and 589 are applied to the surfacesopposite to the surfaces that are coupled to the dielectric layer 578 onboth the top and bottom conductive layers 575 and 576.

It should be noted that the present embodiments should not be limited toconnecting the sensor elements of the rows using vias to the bottomconductive layer 576, but may include connecting the sensor elements ofthe columns using vias to the bottom conductive layer 576.

When pins are not being sensed (only one pin is sensed at a time), theyare routed to ground. By surrounding the sensing device (e.g.,touch-sensor pad) with a ground plane, the exterior elements have thesame fringe capacitance to ground as the interior elements.

In one embodiment, an IC including the processing device 210 may bedirectly placed on the non-sensor side of the PCB. This placement doesnot necessary have to be in the center. The processing device IC is notrequired to have a specific set of dimensions for a touch-sensor pad,nor a certain number of pins. Alternatively, the IC may be placedsomewhere external to the PCB.

FIG. 6 illustrates a block diagram of one embodiment of a sensing deviceincluding a switch circuit. Sensing device 610 includes switch circuit620 and a plurality of sensor elements 601(1)-601(N), where N is apositive integer value representative of a total number of the pluralityof sensor elements of the sensing device 610. Sensor elements601(1)-601(N) are coupled to the switch circuit 620. Sensing device 610is coupled to processing device 210. In particular, processing device210 includes a plurality of pins 602(1)-602(1), where L is a positiveinteger value equal to the number of pins, and the switch circuit 620 iscoupled to the plurality of pins 602(1)-602(L).

Sensor elements 601(1)-601(N) are illustrated as vertical barsrectangular shaped bars. It should be noted that other shapes may beused for the sensor elements, such as diamond shapes, as describedabove. These sensor elements 601(1)-601(N) may be part of amulti-dimension sensor array, or alternatively, of a single dimensionsensor array. The sensor array may be one dimensional, detectingmovement in one axis. The sensor array may also be two dimensional,detecting movements in two axes. The multi-dimension sensor arraycomprises a plurality of sensor elements, organized as rows and columns,and may be used in a touch-sensor pad (e.g., 220). The single-dimensionsensor array comprises a plurality of sensor elements, organized asrows, or alternatively, as columns, and may be used in a touch-sensorslider (e.g., 230).

Sensor elements 601(1)-601(N) are configured to detect a presence of aconductive object 303 on the sensing device 610. The switch circuit 620is configured to group the plurality of sensor elements 601(1)-601(N)into multiple first scan groups and a second scan group.

The processing device 210 includes one or more capacitance sensors 201coupled to the circuit switch 620 via pins 602(1)-602(L). Thecapacitance sensors are configured to measure capacitance on theplurality of sensor elements 601(1)-601(N).

The switch circuit may include first and second settings. The firstsetting is configured to couple each capacitance sensor of the one ormore capacitance sensors of the processing device 210 to a first scangroup of the multiple first scan groups. Each sensor element of the eachfirst scan group is coupled together. The second setting is configuredto couple the one or more capacitance sensors to two or more sensorelements of a selected first scan group.

Each first scan group includes a number of sensor elements that is equalto √{square root over (N)}, where N is a positive integer valuerepresentative of a total number of the plurality of sensor elements601(1)-601(N) of the sensing device 610. Accordingly, the embodimentsdescribed herein may include the advantage of reducing an average scanrate to detect the position of the conductive object on the sensingdevice. In one exemplary embodiment, the processing device 210 isconfigured to detect the average scan rate to detect the position isapproximately (2√{square root over (N)}+1)/2 Unlike the conventionaldesign, which locates the contacting point of the conductive object in(N+1)/2 using a linear search algorithm, the embodiments describedherein include N number or sensor elements grouped into √{square rootover (N)}, each group having √{square root over (N)} sensor elements. Inthe first scan, maximally √{square root over (N)} cycles are needed toscan √{square root over (N)} groups (e.g., coarse scan). In the secondscan, maximally √{square root over (N)} cycles are needed to scan√{square root over (N)} sensor elements (e.g., fine scan). Accordingly,the scan rate is 2√{square root over (N)}. In another embodiment, theswitch circuit is configured to dynamically partition the second scangroup (e.g., fine scan group) such that the contact point (e.g., sensorelement that detects the presence of the conductive object) is in thecenter of the second scan group. In this embodiment, the average scanrate is approximately (2√{square root over (N)}+1)/2.

In another embodiment, the processing device 210 may perform a firstscan, on average, in approximately (√{square root over (N)}+1)/2, andthe second scan, on average, in approximately (√{square root over(N)}+1)/2, resulting in an average scan rate of approximately (2√{squareroot over (N)}+1)/2.

FIG. 7A illustrates a block diagram of one exemplary embodiment of aswitch circuit. The switch circuit 720 is coupled to 4 sensor elements701(1)-701(4) of sensing device 610, and two capacitance sensors703(1)-703(2) of processing device 210 via pins 702(1) and 702(2). Theprocessing device 210 is configured to detect the presence of theconductive object 303 on the sensing device 610. To detect the presenceof the conductive object 303, the processing device 210 may sequentiallyscan the sensor elements 701(1)-701(4) to determine the capacitancevariation on the sensor elements to detect the presence and/or theposition of the conductive object 303 on the sensing device 610. Theswitch circuit 720 may be configured in first or second settings 710 and720, respectively. First setting 710 and second setting 730 areillustrated and described with respect to FIG. 7B and FIG. 7C,respectively.

FIG. 7B illustrates a block diagram of the switch circuit of FIG. 7A ina first setting. In first setting 710, switch circuit 720 is configuredto couple capacitance sensors 703(1) and 703(2) to groups of sensorelements, groups 704 and 705. The first group 704 includes the first andsecond sensor elements 701(1) and 701(2). The second group 705 includesthe third and fourth sensor elements 701(3) and 701(4). During the firstscan, the sensor elements of each group are coupled together (e.g.,coupled to the same capacitance sensor). The processing device 210 scansthe two groups 704 and 705 during the first scan using capacitancesensors 703(1) and 703(2), and detects the presence of the conductiveobject 303 in the first area using the capacitance sensors 703(1) and703(2). The first area is less than the area of the sensing device. Inparticular, the first area is the area of the group (e.g., 704) thatdetects the presence of the conductive object 303. The processing device210 then selects the capacitance sensor (e.g., in this case, capacitancesensor 703(1)) coupled to the group (e.g., 704) that includes the firstarea in which the presence of the conductive object 303 is detectedusing the first scan. Alternatively, the processing device 210 selectsthe group that includes the first area in which the presence of theconductive object is detected using the first scan. Informationregarding which capacitance sensor or group is selected may be used bythe second setting for the second scan, described below.

FIG. 7C illustrates a block diagram of the switch circuit of FIG. 7A ina second setting. In second setting 730, switch circuit 720 isconfigured to couple the capacitance sensors 703(1) and 703(2) to thetwo sensor elements 701(1) and 701(2), respectively, of the selectedgroup 707. The selected group 707 may be determined using theinformation obtained during the first scan regarding the selected groupor selected capacitance sensor. In one embodiment, the selected group707 includes the same sensor elements of the group that detected thepresence of the conductive object 303 on the sensing device 610 (e.g.,group 704). Alternatively, the selected group of sensor elements mayinclude sensor elements that surround the sensor element that detectedthe presence of the conductive object 303, even though one or more ofthese sensors may belong to a different group during the first scan. Theselected group 707 includes the first and second sensor elements 701(1)and 701(2). During the second scan, the sensor elements of each groupare not coupled together (e.g., not coupled to the same capacitancesensor), but are coupled to individual capacitance sensors. Inparticular, capacitance sensor 703(1) is coupled to sensor element701(1), and capacitance sensor 703(2) is coupled to sensor element701(2). The processing device 210 scans the two sensor elements 701(1)and 701(2) during the second scan using capacitance sensors 703(1) and703(2), and detects the presence of the conductive object 303 within thefirst area using the capacitance sensors 703(1) and 703(2). Theprocessing device 210 then selects the capacitance sensor (e.g., in thiscase, capacitance sensor 703(2)) coupled to the sensor element (e.g.,701(21) on which the presence of the conductive object 303 is detectedusing the second scan.

FIG. 8A illustrates a block diagram of another exemplary embodiment of aswitch circuit. The switch circuit 820 is coupled to 9 sensor elements801(1)-801(9) of sensing device 610, and three capacitance sensors803(1)-803(8) of processing device 210 via pins 802(1)-802(3). Theprocessing device 210 is configured to detect the presence of theconductive object 303 on the sensing device 610. To detect the presenceof the conductive object 303, the processing device 210 may sequentiallyscan the sensor elements 801(1)-801(9) to determine the capacitancevariation on the sensor elements to detect the presence and/or theposition of the conductive object 303 on the sensing device 610. Theswitch circuit 820 may be configured in first or second settings 810 and820, respectively. First setting 810 and second setting 820 areillustrated and described with respect to FIG. 8B and FIG. 8C,respectively.

FIG. 8B illustrates a block diagram of the switch circuit of FIG. 8A ina first setting. In first setting 810, switch circuit 820 is configuredto couple capacitance sensors 803(1)-803(3) to groups of sensorelements, groups 804, 805, and 806, respectively. The first group 804includes the first, second, and third sensor elements 801(1)-801(3). Thesecond group 805 includes the fourth, fifth, and sixth sensor elements801(4)-801(6). The third group 806 includes the seventh, eighth, andninth sensor elements 801(7)-801(9). During the first scan, the sensorelements of each group are coupled together (e.g., coupled to the samecapacitance sensor), the processing device 210 scans the three groups804, 805, and 806 during the first scan using capacitance sensors803(1)-803(3), and detects the presence of the conductive object 303 inthe first area using the capacitance sensors 803(1)-803(3). The firstarea is less than the area of the sensing device. In particular, thefirst area is the area of the group (e.g., 805) that detects thepresence of the conductive object 303. The processing device 210 thenselects the capacitance sensor (e.g., in this case, capacitance sensor803(2)) coupled to the group (e.g., 805) that includes the first area inwhich the presence of the conductive object is detected using the firstscan. Alternatively, the processing device 210 selects the group thatincludes the first area in which the presence of the conductive objectis detected using the first scan. Information regarding whichcapacitance sensor or group is selected may be used by the secondsetting for the second scan, described below.

FIG. 8C illustrates a block diagram of the switch circuit of FIG. 8A ina second setting. In second setting 830, switch circuit 820 isconfigured to couple the capacitance sensors 803(1)-803(3) to the threesensor elements 801(1)-801(3), respectively, of the selected group 807(e.g., fine scan group). The selected group 807 may be determined usingthe information obtained during the first scan regarding the selectedgroup or selected capacitance sensor. In one embodiment, the selectedgroup 807 includes the same sensor elements of the group that detectedthe presence of the conductive object 303 on the sensing device 610(e.g., group 805). Alternatively, the selected group of sensor elementsmay include sensor elements that surround the sensor element thatdetected the presence of the conductive object 303, even though one ormore of these sensors may belong to a different group during the firstscan. The selected group 807 includes the fourth, fifth, and sixthsensor elements 801(3)-801(6). During the second scan, the sensorelements of each group are not coupled together (e.g., not coupled tothe same capacitance sensor), but are coupled to individual capacitancesensors. In particular, capacitance sensor 803(1) is coupled to sensorelement 801(4), capacitance sensor 803(2) is coupled to sensor element801(5), and capacitance sensor 803(2) is coupled to sensor element801(6). The processing device 210 scans the three sensor elements801(4), 801(5), and 801(6) during the second scan using capacitancesensors 803(1), 803(2), and 803(3), and detects the presence of theconductive object 303 within the first area using the capacitancesensors 803(1), 803(2), and 803(3). The processing device 210 thenselects the capacitance sensor (e.g., in this case, capacitance sensor803(2)) coupled to the sensor element (e.g., 801(5)) on which thepresence of the conductive object 303 is detected using the second scan.

FIG. 9A illustrates a block diagram of another exemplary embodiment of aswitch circuit. The switch circuit 920 is coupled to 9 sensor elements901(1)-901(9) of sensing device 610, and three capacitance sensors903(1)903(8) of processing device 210 via pins 902(1)-902(3). Theprocessing device 210 is configured to detect the presence of theconductive object 303 on the sensing device 610. To detect the presenceof the conductive object 303, the processing device 210 may sequentiallyscan the sensor elements 901(1)-901(9) to determine the capacitancevariation on the sensor elements to detect the presence and/or theposition of the conductive object 303 on the sensing device 610. Theswitch circuit 920 may be configured in first or second settings 910 and920, respectively. First setting 910 and second setting 920 areillustrated and described with respect to FIG. 9B and FIG. 9C,respectively.

FIG. 9B illustrates a block diagram of the switch circuit of FIG. 9A ina first setting. In first setting 910, switch circuit 920 is configuredto couple capacitance sensors 903(1)-903(3) to groups of sensorelements, groups 904, 905, and 906, respectively. The first group 904includes the first, second, and third sensor elements 901(1)-901(3). Thesecond group 905 includes the fourth, fifth, and sixth sensor elements901(4)-901(6). The third group 906 includes the seventh, eighth, andninth sensor elements 901(7)-901(9). During the first scan, the sensorelements of each group are coupled together (e.g., coupled to the samecapacitance sensor). The processing device 210 scans the three groups904, 905, and 906 during the first scan using capacitance sensors903(1)-903(3), and detects the presence of the conductive object 303 inthe first area using the capacitance sensors 903(1)-903(3). The firstarea is less than the area of the sensing device. In particular, thefirst area is the area of the group (e.g., 805) that detects thepresence of the conductive object 303. The processing device 210 thenselects the capacitance sensor (e.g., in this case, capacitance sensor803(2)) coupled to the group (e.g., 805) that includes the first area inwhich the presence of the conductive object is detected using the firstscan. Alternatively, the processing device 210 selects the group thatincludes the first area in which the presence of the conductive objectis detected using the first scan. Information regarding whichcapacitance sensor or group is selected may be used by the secondsetting for the second scan, described below.

FIG. 9C illustrates a block diagram of the switch circuit of FIG. 9A ina second setting. In second setting 930, switch circuit 920 isconfigured to couple the capacitance sensors 903(1)-903(3) to the threesensor elements 801(1)-801(3), respectively, of the selected group 907(e.g., fine scan group). The selected group 907 may be determined usingthe information obtained during the first scan regarding the selectedgroup or selected capacitance sensor. In one embodiment, the selectedgroup 907 includes the same sensor elements of the group that detectedthe presence of the conductive object 303 on the sensing device 610(e.g., group 904). Alternatively, the selected group of sensor elementsmay include sensor elements that surround the sensor element thatdetected the presence of the conductive object 303, even though one ormore of these sensors may belong to a different group during the firstscan. The selected group 907 includes the first, second, and thirdsensor elements 801(1)-801(3). During the second scan, the sensorelements of each group) are not coupled together (e.g., not coupled tothe came capacitance sensor), but are coupled to individual capacitancesensors. In particular, capacitance sensor 903(1) is coupled to sensorelement 901(1), capacitance sensor 903(2) is coupled to sensor element901(2), and capacitance sensor 903(2) is coupled to sensor element901(3). The processing device 210 scans the three sensor elements901(1), 901(2), and 901(3) during the second scan using capacitancesensors 903(1), 903(2), and 903(3), and detects the presence of theconductive object 303 within the first area using the capacitancesensors 903(1), 903(2), and 903(3). The processing device 210 thenselects the capacitance sensor (e.g., in this case, capacitance sensor903(3)) coupled to the sensor element (e.g., 901(3)) on which thepresence of the conductive object 303 is detected using the second scan.

In the previous embodiment, the processing device selected group 904 asthe group that included the area in which the presence of the conductiveobject 303 is detected. Because the conductive object 303 is between thefirst and second groups 904 and 905, the processing device 210, inanother embodiment, may select group 905, and detect that the presenceof the conductive object 303 is on sensor element 901(4), similarly todetecting the conductive object on 901(3) as described above.

FIG. 9D illustrates a block diagram of the switch circuit of FIG. 8A ina second setting. In second setting 940, switch circuit 920 isconfigured to couple the capacitance sensors 903(1)-903(3) to the threesensor elements 801(2)-801(4), respectively, of the selected group 908(e.g., fine scan group). As previously mentioned, the selected group 908may be determined using the information obtained during the first scanregarding the selected group or selected capacitance sensor. Forexample, if the conductive object 303 is detected by 2 adjacent groups,groups 904 and 905, then it can be determined that the presence of theconductive object 303 is located in the middle, between groups 904 and905. Using this information, the selected group 908 may be dynamicallygrouped to include sensor elements from both group 904 and group 905,placing the selected group 908 in the middle, between groups 904 and905. In this particular embodiment, the switch circuit 920 dynamicallypartitions the selected group 908. In other words, instead of using thesensor elements of only one of the groups (e.g., 901(1)-901(3) of group904, or 901(4)-901(6) of group 905) that detected the conductive object303 in the first scan (as described with respect to FIG. 9C), the switchcircuit 920 couples the selected group 908 to include sensor elements901(2)-901(4), such that the presence of the conductive object 303 is inthe center of the selected group 908 (e.g., between groups 904 and 905of the first scan. Accordingly, capacitance sensor 903(1) is coupled tosensor element 901(2), capacitance sensor 903(2) is coupled to sensorelement 901(3), and capacitance sensor 903(3) is coupled to sensorelement 901(4). In another embodiment, the switch circuit 920 may beconfigured in other configurations, such as coupling sensor elements901(3)-901(5) to capacitance sensors 903(1)-903(3), respectively.

The embodiments described herein are not limited to include threecapacitance sensors, or nine sensor elements, but may include any numberof capacitance sensors and sensor elements. It should also be noted thatthe operations of processing device 210, described with respect to FIGS.7A-7C, 8A-8D, and 9A-9D, may also be performed by a processing device ofthe host 250 (e.g., host processor), drivers of the host 250, theembedded controller 260, or by hardware, software, and/or firmware ofother processing devices.

Unlike the conventional touch-sensor pads, in one embodiment, the switchcircuit may facilitate a scan rate or speed at which the touch-sensorpad locates the position of the presence of the conductive object on thesensing device of less than approximately 30 (ms) (e.g., to complete onescan). In another embodiment, the switch circuit may facilitate a scanrate of less than approximately 12.5 ms. In another embodiment, theswitch circuit may facilitate, a scan rate of less than approximately 10ms. Accordingly, a user will not notice the position “jumps” in thecursor with scan rates less than the minimum sample rate for theparticular interface. Further, by reducing the scan rate, the likelihoodof bottleneck in the interface is less likely to occur in datacommunication between the user interface device and the host.

In one embodiment, the method may include detecting a presence of aconductive object in a first area of a sensing device using a first scanof the sensing device, and detecting the presence of the conductiveobject to determine a position of the conductive object within the firstarea using a second scan of the first area of the sensing device. Thefirst area may be less than an entire area of the sensing device.Detecting the presence of the conductive object in the first area mayinclude, first, grouping a plurality of sensor elements of the sensingdevice into a plurality of first scan groups, each including two or moresensor elements coupled together during the first scan. Second, themethod includes scanning the first scan groups during the first scanusing one or more capacitance sensors coupled to each of the first scangroups, and detecting the presence of the conductive object on one ofthe first scan groups using the first scan. After the presence of theconductive object is detecting in the first area during the first scan,then the presence of the conductive object is detected to determine theposition of the conductive object within the first area. This may bedone by, first, grouping two or more sensor elements of the sensingdevice into a second scan group, which includes the two or more sensorelements of the one first scan group that detected the presence of theconductive object (e.g., selected group). Second, the method furtherincludes scanning the second scan group during the second scan using theone or more capacitance sensors coupled to the second scan group, anddetecting the presence of the conductive object on the one sensorelement of the two or more sensor elements of the second scan groupusing the second scan.

In another embodiment, the method for detecting the presence of theconductive object to determine the position of the conductive objectwithin the first area may include, first, detecting the presence of theconductive object on two of the first scan groups using the first scan.After the presence of the conductive object is detecting in the firstarea during the first scan, then the presence of the conductive objectis detected to determine the position of the conductive object withinthe first area. This may be done by, first, grouping two or more sensorelements of the sensing device into a second scan group, which includessensor elements from the two first scan groups that detected thepresence of the conductive object. The method also includes scanning thesecond scan group during the second scan using the one or morecapacitance sensors coupled to the second scan group, and detecting thepresence of the conductive object on one sensor element of the two ormore sensor elements of the second scan group using the second scan.

In one embodiment, the method of detecting the presence of theconductive object in the first area using the first scan includesgrouping a plurality of sensor elements of the sensing device into aplurality of first scan groups. Each first scan group includes two ormore sensor elements each coupled to a capacitance sensor. The methodfurther includes scanning the first scan groups during the first scanusing capacitance sensors coupled to each first scan group, anddetecting the presence of the conductive object on one of the first scangroups using the first scan, which may include determining a sensorelement of the one first scan group that detected the presence of theconductive object, grouping the plurality of sensor elements of thesensing device into a second scan group, wherein the second scan groupcomprises the determined sensor element and two or more sensor elementsadjacent to the determined sensor element of the one first scan groupthat detected the presence of the conductive object; scanning the secondscan group during the second scan using capacitance sensors coupled tothe second scan group, and detecting the presence of the conductiveobject on the one sensor element of the second scan group using thesecond scan.

In another embodiment, the operation of detecting the presence of theconductive object in the first area using the first scan includesscanning two or more first scan groups of sensor elements during thefirst scan. Each first scan group of sensor elements may be separatelyscanned during the first scan, and each first scan group comprises twoor more sensor elements may be coupled together during the first scan.The operation may further include determining the first area in whichthe presence of the conductive object is detected based on the firstscan.

The operation of detecting the presence of the conductive object todetermine the position of the conductive object within the first areausing the second scan of the first area of the sensing device mayinclude selecting a second scan group that includes the first area inwhich the presence of the conductive object is detected during the firstscan. The second scan group includes two or more sensor elements. Theoperation may further include scanning the two or more sensor elementsof the selected second scan group that includes the first, area duringthe second scan. Each sensor element of the two or more sensor elementsmay be separately scanned during the second scan. The operation mayfurther include selecting a sensor element of the two or more sensorelements of the selected second scan group that includes the detectedpresence of the conductive object based on the second scan.

The operation of scanning the two or more first scan groups of sensorelements during the first scan includes coupling one or more capacitancesensors to the two or more groups. Each sensor element of each group maybe coupled to a same capacitance sensor of the one or more capacitancesensors. In one embodiment, the number of capacitance sensors is equalto the square root of the number of sensor elements of the sensingdevice (e.g., √{square root over (N)}). The number of each first scangroup and the second scan group may be equal to the square root of thenumber of sensor elements of the sensing device (e.g., √{square rootover (N)}). Alternatively, any number, and any combination ofcapacitance sensors, and sensor elements in the first and second scangroups may be used.

The operation of scanning two or more sensor elements of the selectedfirst scan group during the second scan may include coupling the one ormore capacitance sensors to the two or more sensor elements of theselected first scan group. Alternatively, the operation may includecoupling the one or more capacitance sensors to two or more sensorelements of a second scan group. The second scan group may includesensor elements of one or more first scan group. The second scan groupmay include sensor elements of two adjacent first scan groups.

It should be noted that scanning the plurality of sensor elements may bedone using one or more capacitance sensors, in one exemplary embodiment,one capacitance sensor may be multiplexed to connect to the sensorcircuit, which determines which sensor element is being measured.Alternatively, two or more capacitance sensors may be used, with orwithout a multiplexer, to measure the capacitance on the plurality ofsensor elements.

Embodiments of the present invention, described herein, include variousoperations. These operations may be performed by hardware components,software, firmware, or a combination thereof. As used herein, the term“coupled to” may mean coupled directly or indirectly through one or moreintervening components. Any of the signals provided over various busesdescribed herein may be time multiplexed with other signals and providedover one or more common buses. Additionally, the interconnection betweencircuit components or blocks may be shown as buses or as single signallines. Each of the buses may alternatively be one or more single signallines and each of the single signal lines may alternatively be buses.

Certain embodiments may be implemented as a computer program productthat may include instructions stored on a machine-readable medium. Theseinstructions may be used to program a general-purpose or special-purposeprocessor to perform the described operations. A machine-readable mediumincludes any mechanism for storing or transmitting information in a form(e.g., software, processing application) readable by a machine (e.g., acomputer). The machine-readable medium may include, but is not limitedto magnetic storage medium (e.g., floppy diskette); optical storagemedium (e.g., CD-ROM); magneto-optical storage medium; read-only memory(ROM); random-access memory (RAM); erasable programmable memory (e.g.,EPROM and EEPROM); flash memory; electrical, optical, acoustical, orother form of propagated signal (e.g., carrier waves, infrared signals,digital signals, etc.); or another type of medium suitable for storingelectronic instructions.

Additionally, some embodiments may be practiced in distributed computingenvironments where the machine-readable medium is stored on and/orexecuted by more than one computer system. In addition, the informationtransferred between computer systems may either be pulled or pushedacross the communication medium connecting the computer systems.

Although the operations of the method(s) herein are shown and describedin a particular order, the order of the operations of each method may bealtered so that certain operations may be performed in an inverse orderor so that certain operation may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be in an intermittentand/or alternating manner.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative sense rather than arestrictive sense.

What is claimed is: 1-20. (canceled)
 21. An apparatus comprising: acapacitance measurement circuit; and a plurality of sensor elementscoupled to the capacitance measurement circuit, the plurality of sensorelements corresponding to a first and second area on a surface, whereinthe capacitance measurement circuit is configured to measure capacitanceof the first area in a first mode and to measure capacitance of thesecond area in a second mode.
 22. The apparatus of claim 21, whereineach of the plurality of sensor elements are coupled to pins of thecapacitance measurement circuit.
 23. The apparatus of claim 21, whereinthe capacitance measurement circuit is disposed on an integratedcircuit.
 24. The apparatus of claim 21, wherein the plurality of sensorelements is arranged in an array of rows and an array of columns. 25.The apparatus of claim 24, wherein the plurality of sensor elementssubstantially covers an area defined by a user interface.